Galaxy and Space Physics

Contents

In ASG’s universe interplanetary and interstellar distances are not an issue thanks to the hyperspace field that lets ships travel instantaneously between pairs of related jump-points. However orbital mechanics rule in all other flight phases and in effect “DeltaV” is the primary metric to evaluate trips and ship endurance.

The game takes place in the “Quadrans” galaxy, which counts around 8000 stars in 4000 stellar systems in a disk about 12,000 ly in diameter. Its celestial objects are procedurally generated according to a “set of rules” to produce coherent results. Typically orbits must be stable, binary (or higher) stellar systems are common, the radiation from nearby stars is integrated to determine the surface temperatures of planets (and the possibility of liquid water), a giant may migrate toward its star and become a “hot Jupiter”, it may prevent a terrestrial planet from forming and thus generate an asteroid belt instead…

There are about 200 billion stars across 150,000 ly in our galaxy but then again the real universe has lots of RAM!

DeltaV (ΔV) matters more than light years

We are used to evaluate journeys in term of distances but this is not a good metric for space travel. In ASG orbital mechanics do apply and so when orbiting and if submitted to gravity only the conservation of mechanical energy lets you run forever without any effort. Meanwhile you may be covering tremendous distances but are not actually going anywhere.

To adjust their course spaceships apply thrust. Thrust is a force that generates an acceleration (Newton’s second law of motion). Over time acceleration induces a change of velocity called “ΔV = Delta Vee”. Thus at the end of the burn the ship is close to its initial position but now exhibits a different velocity: its orbit has changed. This is demonstrated in the little video below using your ship’s flight planner:

The Spaceships section explains why the remaining on-board propellant mass (the “fuel” expelled by the ship’s engines) is not a convenient measure of the ship’s endurance either. As a result ΔV is the primary metric used by your on-board avionics.

ΔV matters for jumps too

Mechanical energy is not conserved during jumps but the hyperspace field and momentum are. In effect spaceships retain their velocity through jumps. As a consequence the orbital velocity at the jump-exit point is the sum of the velocity at the entry point and of the relative motion between the departure and arrival celestial bodies. The latter is labelled “jump ΔV” and has to be dealt with using conventional orbital maneuvering.

The phenomenon is depicted in the example from your flight planner below. At the departure body the dotted gray vector is the ship’s orbital velocity while the white vector represents the motion of the departure body with respect to the arrival. The exit velocity is the sum of these two components (beware that the map view is oriented according to the local equatorial plane so you can use the relative motion vector arrow as a mental reference).

Jump mechanics

Despite centuries of efforts no consistent theory explaining the hyperspace field has been established yet.

In effect jump drives create an anomaly bubble in which the interior space is forced out of the quantum vacuum state. The process is called “jump-space polarization“. The bubble is spherical and centered on the jump drive, and state of the art devices require several hours to expand it (~8 h) so the whole ship is safely contained.

Besides this an hyperspace field is generated by (or at least coincidental to) the local curvature of space time. In classical terms and compared to gravity the hyperspace field exhibits a similar radial symmetry but with different dependencies on mass and distance. Jump-points only exist in pairs (entry and exit) and connect locations around the departure and arrival bodieswhere the hyperspace fields match.

Jump-point pairs exhibit a natural oscillation that is related to their relative motion (jump ΔV) and sometimes called the “hyper-Doppler” effect. For a jump event to occur the anomaly bubble must be excited at a matching phase and frequency (“jump-space modulation“), then released while the jump-point is enclosed. As a result the extension of the jump-space sets the required navigation accuracy for jumps, typically < 100 m. Again the physical process is not really understood but it is generally accepted that the event probably corresponds to “the universe taking a shortcut” to a lower energy state that was disrupted by the anomaly.

Due to the shape of the hyperspace field mechanical energy is not conserved during a jump. However momentum is and consequently ships retain their velocity. In the respective parent reference frames, the exit velocity thus equals the departure velocity plus the relative motion between the bodies (jump ΔV). Flight planning routines takes these rules into account to discard dangerous solutions leading to unavoidable collisions. More generally they optimize the approaches to jump-points so as to minimize the overall ΔV cost.

Regardless of actually existing hyperspace connections, the maximum jump distance for a given celestial body is set by its mass and the minimum safe approach altitude. On the other hand the minimum jump distance is related to its sphere of influence. Regions where the space time curvature is very complex due to the combined gravity of many surrounding bodies generate evanescent and unreliable jump-points that are automatically discarded by navigation routines.

Jump Explorer tool displaying the long distance jump-points around a gas giant